Looping with while

Computers excel at one thing: doing the same thing over and over without getting bored. A loop is how you write that.

Basic Form

let counter = 0;

while counter < 3 {
    print(counter);
    counter = counter + 1;
}

Output:

0
1
2

How it works:

1. Check the condition counter < 3 — if it's 0 (false), done.
2. Run the block inside the curly braces.
3. Go back to step 1.

while <condition> {
    ...code to repeat...
}

What to Watch Out For

1. Mutation inside the loop

A while loop works by changing the condition. Without counter = counter + 1, the condition counter < 3 will always be true — and the loop will run forever (infinite loop). This is a very common bug!

let i = 0;
while i < 5 {
    print(i);
    // forgot i = i + 1 → the program will never finish!
}

So: make sure there's something in the block that eventually makes the condition false.

2. It can use any variable

The condition doesn't have to be a number that goes up — it can be any expression:

let skor = 100;
while skor > 0 {
    print(skor);
    skor = skor - 25;
}
// 100, 75, 50, 25

Using while to Sum

A classic pattern: summing the numbers 1 to 100.

let total = 0;
let i = 1;

while i <= 100 {
    total = total + i;
    i = i + 1;
}

print(total); // 5050

Read it slowly: total accumulates the result each round, i counts until it goes past 100.

Stopping Early with break

Sometimes you want to stop before the condition ends, because of a special situation. Use break:

let i = 0;

while i < 100 {
    i = i + 1;

    if i == 5 {
        break;      // force stop here
    }
}

print(i); // 5

Skipping One Round with continue

continue skips the rest of the code in that round, then jumps straight to the next round:

let i = 0;
let jumlah_genap = 0;

while i < 10 {
    i = i + 1;

    if i % 2 != 0 {
        continue;   // odd numbers are skipped
    }

    jumlah_genap = jumlah_genap + i;
}

print(jumlah_genap); // 2 + 4 + 6 + 8 + 10 = 30

Exercises

1. Print the numbers 10 down to 1 (backwards).
2. Compute and print the sum of all even numbers from 1 to 20.
3. Print all divisors of the number 60 (numbers where 60 % b == 0), starting from b = 1 up to b = 60.
4. Use while to reduce the value of nilai to 0 through repeated subtraction, and count how many steps it takes.

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